1. Field of the Invention
The present invention relates to a method of communication suitable for use in, for example, a base station and a terminal apparatus in a radio telephone system, and to a base station and a terminal apparatus to which the method of communication is applied
2. Description of the Related Art
In a mobile communication such as a radio telephone system or the like, multiple access is provided wherein a plurality of mobile stations (terminal apparatuses or subscribers) have access to a single base station. In this case, a predetermined transmission band is allocated in advance to each base station; a plurality of transmission channels are set in the transmission band; in the case of a request for communication or the like from each terminal apparatus, any of the transmission channels can be allocated to the terminal apparatus; and the terminal apparatus side initiates communication by way of the base station using the allocated transmission channel.
For example, such systems of communication wherein the transmission channels are set include a frequency division multiple access (FDMA), a time division multiple access (TDMA), a code division multiple access (CDMA) and so on.
Referring to each method, in an FDMA communication system a plurality of transmission channels are provided by dividing the transmission band by a unit of frequency. In a TDMA communication system a transmission channel is divided by a predetermined time unit to form a plurality of time slots within a single transmission channel, each of the time slots being allocated to the terminal equipments to be linked. Therefore, it is possible to link the plurality of terminal equipment using the single transmission channel. In a CDMA communication system of a specified code is allocated to each of the terminal equipments and a carrier having the same frequency is subjected to spectrum spread modulation by the code for transmitting it to the base station. The receiving side achieves synchronization with each code to identify a signal from a desired terminal apparatus.
In the following description, a communication line set between a single terminal apparatus and a base station is referred to as one transmission channel. Therefore, in the case of the TDMA system, a time slot allocated to a terminal apparatus is logically one transmission channel and, in the case of the CDMA system, the transmission of a signal spread into a code allocated to a terminal apparatus is logically one transmission channel.
Meanwhile, in a radio telephone system, a transmission capacity which can be transmitted through one transmission channel has been fixed regardless of the system used for setting the transmission channels in any system, and it has not been possible to change the transmission capacity depending on the type of the data to be transmitted. For example, to transmit image data for facsimile during an on-going audio call using a terminal apparatus which is a portable telephone, it has been necessary to transmit the image data instead of audio data with the audio call interrupted temporarily and it has not been possible to transmit the image data from the portable telephone concurrently with the transmission of the audio data.
Meanwhile, a capability of transmitting various data other than audio data utilizing a wireless terminal such as a portable telephone or the like has recently been coming into practice. However, when only one type of data of a fixed capacity can be transmitted through one transmission channel, it is necessary to interrupt the transmission of data of other types or to re-perform a process of connecting the line each time the type of data is transmitted. This has made a transmission process cumbersome and not preferred from the viewpoint of efficiency of use of a communication line.